There has been known a document reading device having a light source that emits light from the outside of document area toward a document edge and another light source that emits light from the document area toward the document edge. When detecting a leading edge and a trailing edge of the document, the document reading device selectively turns on one of the two light sources so as to form a short shadow at the document edge to be detected. The document reading device determines the document edge according to the detected short shadow formed by the lighting.
Other than the above configuration, there is also known another reading device having a light source that emits light in a single direction toward the document.